303
FXUS65 KCYS 282133
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
333 PM MDT Fri Jun 28 2024

.KEY MESSAGES...

- Active weather pattern ahead, with a cooling trend possible
  next week due to several passing cold fronts.

&&

.SHORT TERM /THROUGH SUNDAY NIGHT/...
Issued at 159 PM MDT Fri Jun 28 2024

Radar continues to be quiet, only showing a few lonely blobs across
the southern Nebraska panhandle. Hi-Res guidance continues to trend
precipitation downwards, however, severe weather still cannot be
ruled out with the RAP showing a bubble of 2000 J/kg of CAPE later
this afternoon in Kimball and Cheyenne Counties. Being in the
right entrance region of a 250 mb jet streak and and forcing
from an incoming secondary cold front should provide the
necessary lift, however, the better environment looks south of
the Nebraska/Colorado border. If storms do develop, they should
dissipate by this evening.

Quiet weather is expected on Saturday as brief ridging passes over
the Rockies. For the most part, this should keep storms at bay,
however, a weak disturbance aloft could spark some convection
along the high terrain. Temperatures behind the cold front will
be about 10 degrees cooler compared to Friday, so mainly looking
at highs in the mid 70s to low 80s.

More severe weather is possible on Sunday as the ridge slides
eastwards and a trough begins to enter western CONUS. Southwest flow
aloft will usher in a plume of moisture east of the Laramie Range.
Combined with more southerly surface flow into the panhandle, PWs
will be over an inch, which is roughly the 90th percentile for this
time of year. This will likely lead to heavy rain in storms Sunday
afternoon. As mentioned, severe weather could be possible with a
weak shortwave passing overhead. Currently, it appears more like a
wind threat on Sunday with DCAPE values exceeding 1200 J/kg. Can`t
rule out some large hail with MUCAPE values approaching 1500 J/kg.
Hi-Res guidance shows wide scattered storms throughout the day, so
we`ll have to monitor most of the CWA.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
Issued at 315 PM MDT Fri Jun 28 2024

Medium range models in good agreement with the overall weather
pattern through Wednesday, but then models diverge significantly
late this week...including Independence Day. Starting on Monday,
models indicate another Pacific upper level trough and
associated cold front pushing southeast across Wyoming and
western Nebraska late in the day after the brief warm up on
Sunday. Another round of windy conditions are possible,
especially west of I-25, as the cold front slides east across
the area. Not expecting High Wind criteria (40+ mph
sustained/58+ mph gusts) at this time, but a few recent events
have overperformed, so will have to keep an eye on this one for
mainly Monday morning through mid Monday afternoon. Thunderstorm
probabilities actually look lower on Monday due to dry westerly
winds and substantial mid to high cloud cover shown by most
deterministic models and also the majority of ensembles as the
cold front moves into the area. Kept POP between 15 to 25
percent for most areas with higher coverage/chances in the
mountains and east central Wyoming/northern Nebraska Panhandle.

Slightly cooler weather is expected for Tuesday and Wednesday as
most models show northwest flow aloft and east to southeast
winds at the surface. However, afternoon temperatures should
still be seasonable for this time of the year with highs in
upper 70s to middle 80s. Models and ensemble are hinting at a
lower coverage of showers and thunderstorms across the area,
even with the natural convergence zone along the Laramie Range.
Further analysis indicates relatively low PWAT for this time of
the year across southeast Wyoming with values around 0.40 to
0.60 inches. Granted, this is enough for thunderstorm initiation
but strong to severe storms look unlikely at this time and
limited to gusty outflow winds. Lower PWATs are likely due to
the progressive west to northwest flow across the Pac NW and
northern/central plains, with poor moisture transport from the
Gulf of Mexico. Will continue to keep an eye on this since
northwest flow in July can lead to some pretty big severe
weather events, but without the moisture, kept POP below 25
percent for now.

For later in the week, large ensemble spreads exist for both
precipitation and especially temperatures. Deterministic models
show a pretty strong upper level shortwave trough digging south
into the northern high plains on Independence Day/Thursday.
Models all show 700mb temperatures as low as 0c to 4c as the
cold front pushes south into northern Wyoming Thursday morning.
Will need to monitor this front due to the possibility of late
night/early morning convection possible across the plains, and
much cooler temperatures for July 4th celebrations. With
significant timing differences and ensemble spreads, not very
confident in either of these scenarios, so kept highs in the 80s
with a mention of thunderstorms north of Interstate 80 for now.

Further out, all long range models seem to come into better
agreement after day 7...showing a strong 600dm upper level high
forming over the western Great Basin Region. Hot temperatures
are possible across the whole forecast area next weekend.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1140 AM MDT Fri Jun 28 2024

A stationary front near the Laramie Range/I-25 corridor this morning
will lift northeast as a warm front this afternoon, while a strong cold
front, for this time of the year, will move southeast across the area
tonight. This frontal system may aid in shower and thunderstorm develop
late this afternoon through early this evening, but coverage appears
limited to western Nebraska at this time.

HAZARDS/WEATHER TRENDS: VFR conditions will prevail over the next 24
hours. Kept VCTS in the western Nebraska TAFs due to the relatively low
coverage of thunderstorms and limited confidence this afternoon.
Surface winds are forecast to shift into the north late this afternoon
and tonight as the cold front moves through, with breezy conditions
possible after 03z.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...None.
NE...None.

&&

$$

SHORT TERM...SF
LONG TERM...TJT
AVIATION...TJT